1. Field of the Invention
The present invention relates to a content-data playback system enabling playback of content data while eliminating fraudulent use thereof, and a recording device used thereto.
2. Description of the Related Art
Recently, content-distributing systems which distribute computerized content, such as books, newspapers, music, or motion pictures, to user terminals to allow users to view such content become widespread in accordance with the development of information societies.
However, computerized content (hereinafter, simply called “content”) can be easily replicated, so that misconduct disregarding copyrights thereof is likely to happen. In general, from the standpoint of protecting content against such misconduct, content is recorded in an encrypted manner by an encryption key, and decrypted when reproduced. An example of such kind of content protection technologies is CPRM (Content Protection for Recordable Media). Moreover, there is proposed an encryption double-key scheme that uses two kinds of keys to doubly encrypt content (see, for example, JP2005-341156A). This kind of encryption double-key scheme is used in, for example, MQbic, (registered trademark). In encryption keys, a key unique to a recording medium, e.g., a medium-unique key is stored securely in a secret area in the recoding medium, and is not externally-accessible at all. Therefore, even if, for example, an encrypted content key is solely copied fraudulently, a person who fraudulently copied that key cannot utilize content data without the medium-unique key.
However, if such a medium-unique key is fraudulently read-out through some kind of scheme and is passed to a fraudulent card copying person, it results in cloned cards, made by copying of a legitimate card, floating around, so that fraudulent use of content data may happen.